The present invention relates to a semiconductor memory device the main element of which comprises a field effect transistor of an insulated gate type and, more particularly, to a read-out circuit of a semiconductor memory device in which a high speed read-out operation is required.
The inversion speed of a sense-amplifier output of the conventional semiconductor memory device at a read-out operation depends on the current which flows in the related transistors at the output stage therein. The current flowing in the transistors is governed by the mutual conductance of the memory cells.
However, in the conventional large capacity semiconductor memory device, the mutual conductance of the memory cells tends to be set at a low value for such reasons that the gate width of the memory cell is required to be made as small as possible and that the memory cells are integrated in a stacked or multi-layered construction in order to increase the integration or packing density of the memory cell array.
One of the problems encountered in the conventional memory devices was that it lacked sufficient capacity to drive the inverter amplifier leading to an output buffer and, therefore, the amplitude of the sense-amplifier output voltage had to be large resulting in a low inversion speed of the sense-amplifier output.
Thus, such conventional semiconductor memory devices were not suited for a semiconductor memory device which required a large capacity and a high speed at the read-out operation.